The present invention relates to an electrofusion joint with which members such as polyolefin pipes, in particular, conduits for supplying hot water are joined or connected either to themselves or to the lateral side of other conduits. The present invention also relates to an electrofusion joint fitted with a connecting member for establishing connection to terminals such as nozzles on a conduit header. The present invention further relates to a header for distributing hot water from a heat source providing apparatus such as a hot water supplier to more than one site of use.
Pipes made of crosslinked polyolefins such as silane-crosslinked polyethylene are used as conduits for supplying hot water. Crosslinked polyolefins perform satisfactorily at elevated temperatures as evidenced by high heat resistance and good high-temperature creep characteristic and have a shape-retaining capability. However, unlike non-crosslinked polyolefins, crosslinked polyolefins cannot be fused to members to be joined. Hence, electrofusion joints used to connect non-crosslinked polyolefin pipes are not applicable to crosslinked polyolefin pipes. It is also impossible to form electrofusion joints using crosslinked polyolefins.
Therefore, crosslinked polyolefin pipes are currently joined by means of mechanical couplings, or joints that rely upon mechanical couplings are produced from crosslinked polyolefins. However, mechanical joints used in connecting hot water pipes which require high strength to withstand high operating pressures involve a complicated structure and cannot be handled efficiently in piping work. Further, compressive sealing performed with these mechanical joints causes the disadvantage that their performance will decrease with time as exemplified by deterioration in the reliability of sealing due to creeping in pipes or stress relaxation of pipes and sealants.
Further, if thin-walled resin pipes are connected by conventional electrofusion joints, the joined portions will thermally deform and bulge inwardly to restrict the fluid passage.
An electrofusion joint formed of a thermoplastic resin is known that is provided with a fine orifice in the body of the joint, through which the resin that has become molten when a member of interest is joined by fusion will come out to provide a measure for checking whether said member has completely fused to the joint (see, for example, Unexamined Published Japanese Patent Application No. 61-62696). However, being formed of a kind of thermoplastic resin, this prior art electrofusion joint has the disadvantage that the molten resin coming out of the orifice has the same color as the surrounding resin of which the joint is formed and that extrusion of this resin is difficult to identify. Thus, the time at which fusion has been completed cannot be detected precisely.
Further, connecting terminals such as nozzles on a conduit headers are usually metallic and it is difficult to connect them to crosslinked thermoplastic resin pipes.
FIG. 23 is a diagram showing a piping system for supplying hot water. Shown by 81 in the diagram is a header by which hot water from a heat source providing apparatus 82 such as a hot water supplier is distributed to a faucet 83 in the kitchen, a faucet 84 in the lavatory, a faucet 85 in the bathroom, and other outlets. The heat source providing apparatus 82 receives water from a supply pipe 86, heats it by burning the gas supplied through a gas pipe 87, and supplies the heated water through a hot water main 88 to the header 81.
Header 81 is shaped of a metal in hollow form and has a single receptacle 91 on the inlet side and a plurality of receptacles of same diameter 92a, 92b, 92c, 92d, . . . on the outlet side. The receptacle 91 on the inlet side is connected to the hot water main 88 by fastening means such as screws, whereas the receptacles 92a, 92b, 92c, 92d, . . . on the outlet side are connected to branch pipes 93a, 93b, 93c, 93d, . . . by fastening means such as screws. The branch pipes 93a, . . . have such bore diameters that faucets 83, 84, 85, . . . are supplied with hot water in the necessary flow rates that correspond to the capacities of the respective faucets.
The conventional header 81 has had several problems on account of the fact that it is formed of metal. First, it is liable to corrosion and is heavy. Second, it is difficult to connect to plastic pipes and is not suitable for large-scale production.
Further, the header 81 fitted with a plurality of receptacles of same diameter 92a, . . . on the outlet side has to be connected to branch pipes 93a, . . . of smaller diameter by means of reducers and this has been another factor that makes the header unsuitable for large-scale production.